Chemistry / Unit 7: Chemical Reactions
7.3 Synthesis and Decomposition
Notes
Reactions can be sorted into types by their patterns.
- Synthesis (combination): two or more substances form one product. $\text{A} + \text{B} \rightarrow \text{AB}$. Example: $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$.
- Decomposition: one substance breaks into two or more. $\text{AB} \rightarrow \text{A} + \text{B}$. Example: $2\text{H}_2\text{O} \rightarrow 2\text{H}_2 + \text{O}_2$.
- Many decompositions need energy: heat, electricity or light.
- Metal carbonates decompose into a metal oxide and carbon dioxide: $\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$.
Practice
What type of reaction is $2\text{KClO}_3 \rightarrow 2\text{KCl} + 3\text{O}_2$?
One reactant breaks into two products.
What is the product of the synthesis of calcium and chlorine?
$\text{Ca}^{2+}$ and two $\text{Cl}^-$ give $\text{CaCl}_2$: $\text{Ca} + \text{Cl}_2 \rightarrow \text{CaCl}_2$.
When magnesium carbonate, $\text{MgCO}_3$, is heated, it decomposes. What are the products?
Metal carbonates break down into a metal oxide and carbon dioxide.
Ready for more? Take the Unit 7 test.